The earthquake ______ when I _______some cleaning.

A．starts, was doing

B．started, was doing

C．was starting, was doing

D．starts, were doing

在《中国药典》中，下列药物的含量测定方法是

维生素C（）

A．碘量法

B．非水溶液滴定法

C．旋光度法

D．气相色谱法

E．高效液相色谱法